1. Field of the Invention
This invention relates generally to electrical wiring devices such as electrical switches, receptacles and the like and more particularly to a clamp for back wiring a ground wire to a ground strap.
2. Description of the Prior Art
Electrical switches and receptacles that are used in homes, offices and factories have terminals to which electrical wires are connected by turning a screw down on the wire. The electrical wire is usually a relatively stiff solid wire that must first be shaped into a loop to fit around the mounting screw and then the mounting screw is screw down. The bending of the wire takes time and, if the loop is placed under the screw where the loop is positioned to be turning in a counter-clockwise direction rather than in a clockwise direction, the loop will tend to open up and move out from under the head of the screw as the screw is tightened in a clockwise direction. Additionally, in many instances it is faster and easer to connect a conductor to the rear of a switch or receptacle rather than to a side contact.
Conventional switches and receptacles are provided with compartments located on the side of the device for receiving the electrical conductors of a wiring cable. More specifically, each switch or receptacle is provided with a separate side located screw or clamping device for achieving electrical connection between the individual conductors or wires and the terminal on the switch or receptacle. Normally two wires are present for providing power to the switch or receptacle and a third wire is provided for a ground connection.
As disclosed in U.S. Pat. Nos. 6,188,020 and 5,866,844 to Osterbrock et al., to improve the way that a wire can be connected to a ground strap of a switch or a receptacle, a clamping plate is provided which overlies a base plate. The configuration of the clamping plate facilitates the connection of the ground wire to the ground strap from the rear. Another arrangement for clamping a ground conductor to a ground strap from the rear is disclosed in U.S. Pat. No. 6,293,812 to Ewer et al.
The clamping plate arrangements disclosed in the prior art are generally complex in shape and relatively expensive to manufacture.
What is needed is a new improved clamping plate and ground strap arrangement for connecting a ground wire to a ground terminal from the rear of the switch or receptacle that is simple in design, economical to make and easy to use.
The invention here disclosed is a back wire ground clamp for a wiring device such as a switch or receptacle having a ground strap which supports an outwardly projecting ground lug having a front edge and adapted to receive a ground connection. The ground lug is coupled to a clamp plate by means of a screw which passes through a clearance opening in the clamp plate and is threaded into a receiving opening in the ground lug. The clamp plate supports a blocking tab which extends downward below the front edge of the ground lug and extends side ways for a distance which is less than the length of the front edge of the ground lug. The blocking tab prevents the clamp plate from rotating relative to the ground lug as the screw is tightened and defines an opening between the clamp plate and the ground lug along the front edge of the ground lug into which a single ground wire can be inserted.